1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to an actuator which is actuated by an external input, and more particularly, to an actuator which can remove a particular high frequency component from an external input by providing a low pass filter with a simple change of a mechanical design, and also can reduce or eliminate a tremor or noise caused by a high frequency.
2. Description of Related Art
An actuator may be a driving apparatus with a motor supplied with power to produce a driving force. Also, an actuator, e.g. an optical scanner, may be actuated or vibrated by an external electromagnetic force or other physical forces.
An optical scanner is usually used to change the path of a laser, e.g. during the scanning of a two dimensional image. Such an optical scanner may further be used for a laser printer, a bar code reader, and the like. In addition, the optical scanner may perform more complicated operations such as complex image processing, e.g., for a laser television or the like. In such an environment, a laser may be provided along a certain path as a light source, so that a desired image may be obtained by two-dimensionally changing the path of the laser. A method of using two mirrors, each working with an axis respectively different from each other, has been used to change a laser's path. In addition, another method includes two-dimensionally changing the path of a laser by moving one mirror with two axes.
FIG. 1 is a perspective view illustrating a scanner changing the path of light by moving one mirror with two axes, according to a related art.
Referring to FIG. 1, a scanner 20 includes a mirror 22, a horizontal torsion axis 23, an internal frame 24, a vertical torsion axis 25 and an external frame 26. The mirror 22 is coated to be reflective at the center of the scanner 20. The horizontal torsion axis 23 is extended from the mirror 22 in opposite directions from each other. Here, the internal frame 24 is physically connected to the horizontal torsion axis 23 and is provided around the mirror 22. The vertical torsion axis 25 is extended from the internal frame 24 and perpendicular to the horizontal torsion axis 23. The external frame 26 is physically connected to the vertical torsion axis 25.
Coils 27 are provided on the internal frame 24, which is in a gimbal structure. Accordingly, when a current is supplied to the coils 27, the internal frame 24 may react to an externally formed magnetic field and produce a moment capable of driving the scanner 20. When forming the magnetic field in a tilted direction towards the horizontal torsion axis 23 and the vertical torsion axis 25, and supplying a current to the coils 27, a torque is occurred vertically with respect to the magnetic field and the current. As the occurred torque is divided into two components of the horizontal torsion axis 23 and the vertical torsion axis 25, the mirror 22 may vibrate on the horizontal torsion axis 23. Also, the internal frame 24 and the mirror 22 may vibrate due to vibration on the vertical torsion axis 25. As a result, with such dual-axial vibrations with a single mirror, image signals may be two-dimensionally distributed.
Hereinafter, a dual-axial driving of a mirror will be further described in detail. To project an image on an externally located screen utilizing the scanner 20, scanning lines may be projected on the screen by vibrating the mirror 22 on the vertical torsion axis 25, e.g. vibrating the mirror 22 in a sawtooth wave form of about 60 Hz, and vibrating the mirror 22 on the horizontal torsion axis 23 with a sine wave of about 20 kHz which is a comparatively high frequency. Namely, a high frequency vibration of the horizontal torsion axis 23 may horizontally scan a scanning line on the screen and a low frequency vibration of the vertical torsion axis 25 may vertically move the scanning line on the screen, thereby embodying a two-dimensional image on the screen.
Each moment for vertically and horizontally vibrating the mirror 22 may be provided to the mirror 22 as one synthesized moment. In this instance, such a synthesized moment has an approximate low frequency form in which a form of a high frequency signal is modulated in a low frequency signal.
It is assumed that a resonant frequency of a mass capable of vibrating on the vertical torsion axis 25 of the mirror 22 is designed to be about 1 kHz and a resonant frequency of a mass capable of vibrating on the horizontal torsion axis 23 of the mirror 22 is designed to be about 20 kHz. Under these conditions, when a current of a sawtooth wave of about 60 Hz and a current of a horizontal resonant frequency of about 20 kHz are modulated and supplied to the coils 27 of the internal frame 24, a moment is vertically generated with respect to an externally formed magnetic field. Such a moment is distributed to the horizontal torsion axis 23 and the vertical torsion axis 25, and utilized for actuating the mirror 22. In this instance, since the mirror 22 is oscillated at about 20 kHz on the horizontal torsion axis 23 by the synthesized moment, the mirror 22 does not react to a sawtooth wave component of about 60 Hz and is actuated in a sawtooth wave form of about 60 Hz on the vertical torsion axis 25.
However, such a synthesized moment working on the vertical torsion axis 25 includes a sawtooth component of about 60 Hz and also includes a sine wave component of about 20 kHz. Accordingly, when vertically scanning, a minute tremor or noise of about 20 kHz exists, as shown in FIG. 2. Namely, while each of the vertical torsion axis 25 and the horizontal torsion axis 23 must be independently vibrated by a low frequency signal, e.g. 60 Hz, and a high frequency signal, e.g. 20 kHz, respectively, the high frequency signal affects the low frequency signal of the vertical torsion axis 25, which causes a minute tremor or noise. Referring to FIG. 2, it can be seen that a driving angle of the vertical torsion axis 25 according to a time, i.e. a curve 30, may have a tremor due to a high frequency of about 0.03 degrees.
Such noise may prevent a scanning line from being scanned to a desired location and thus, deteriorate a resolution. Namely, in the case of vertical scanning, horizontal scanning lines may be overlapped due to noise caused by a high frequency, and thus, may not embody a high resolution.
More specifically, when vertically scanning, such noise caused by a high frequency may prevent scanning lines from being scanned in an accurate location. Namely scanning lines may be overlapped with each other or excessively separated from each other. As described above, intervals between horizontal scanning lines may be irregular which may significantly deteriorate a resolution.
Such noise caused by a high frequency tremor described above is a factor to be considered in an actuator requiring a precise location control, such as a scanner. For this reason, a method of constructing a low pass filter as a circuit may be required. However, since electric parts, such as electrical circuitry, may be required, a manufacturing process may be complicated so that productivity is reduced and manufacturing costs are increased.